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Immediately Dangerous to Life or Health Concentrations (IDLH)

Description of substance: Pale-yellow to dark-brown liquid with a garlic-like odor.

LEL: . . Unknown

Original (SCP) IDLH: 20 mg/m3

Basis for original (SCP) IDLH: No useful data on acute inhalation toxicity are available on which to base the IDLH for parathion. If the IDLH were estimated from the statement by AIHA [1971] that "the minimum lethal oral dose for humans has been estimated as ranging from less than 10 mg to 120 mg [Bidstrup 1950; Grob 1950; Hayes 1963]," then an IDLH of 5 mg/m3 would be chosen. This appears to be far too conservative, however, because ACGIH [1971] noted that workers regularly exposed to 2 to 15 mg/m3, with an average concentration of 8 mg/m3, exhibited only a 25% decrease in cholinesterase levels [Kay et al. 1952]. The chosen IDLH, therefore, has been estimated from the female rat oral LD50 of 3 mg/kg cited by ACGIH [1971].

Short-term exposure guidelines: None developed

ACUTE TOXICITY DATA:

Lethal concentration data:

Species

Reference

LC50

LCLo

Time

Adjusted 0.5-hr

LC (CF)

Derived value

Rabbit

G. pig

Mouse

Rat

Deichmann et al. 1952

Deichmann et al. 1952

Izmerov et al. 1982

USAF 1977

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-----

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84 mg/m3

50 mg/m3

14 mg/m3

15 mg/m3

-----

2 hr

2 hr

?

4 hr

80 mg/m3

22 mg/m3

?

168 mg/m3

8.0 mg/m3

2.2 mg/m3

?

17 mg/m3

Lethal dose data:

Species

Reference

Route

LD50

(mg/kg)

LDLo

(mg/kg)

Adjusted LD

Derived value

Mouse

Rabbit

Dog

Cat

Horse

G. pig

Rat

Eto et al. 1966

Kenaga & Morgan 1978

Kenaga & Morgan 1978

Nishizawa et al. 1961

Perkow 1971/1976

von Dozent et al. 1955

Weiss and Orzel 1967

oral

oral

oral

oral

oral

oral

oral

5

10

3

0.93

5

8

2

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-----

-----

-----

-----

-----

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35 mg/m3

70 mg/m3

21 mg/m3

6.5 mg/m3

35 mg/m3

56 mg/m3

14 mg/m3

3.5 mg/m3

7.0 mg/m3

2.1 mg/m3

0.7 mg/m3

3.5 mg/m3

5.6 mg/m3

1.4 mg/m3

Human data: Workers regularly exposed to 2 to 15 mg/m3 (average of 8 mg/m3) exhibited only a 25% decrease in cholinesterase levels [CDC 1956]. The minimum lethal oral dose has been reported to range from 0.17 to 1.471 mg/kg [Arena 1970; CDC 1956; Hartley and Kidd 1986]. [Note: An oral dose ranging from 0.17 to 1.471 mg/kg is equivalent to a worker being exposed to about 8 to 69 mg/m3 for 30 minutes, assuming a breathing rate of 50 liters per minute and 100% absorption.]

Revised IDLH: 10 mg/m3

Basis for revised IDLH: The revised IDLH for parathion is 10 mg/m3 based on chronic inhalation toxicity data in humans [CDC 1956]. This may be a conservative value due to the lack of relevant acute toxicity data in humans exposed to concentrations above 10 mg/m3.